High-Performance Polymer Solar Cells with Minimal Energy Loss Enabled by a Main-Chain-Twisted Nonfullerene Acceptor

We design and synthesize a new main-chain-twisted fused-ring narrow band gap n-type organic semi-conductor acceptor (namely, IE4F-S) with a terminal group on the 4-position of 3-alkylthio-substituted thiophene. The acceptor IE4F-S shows zero ionization potential (IP) offset (Delta IP) with a wide band gap polymer donor PTQ10. Notably, the polymer solar cell (PSC) device operating at such a negligible Delta IP can still yield an outstanding power conversion efficiency (PCE) of 12.20%, with a high open-circuit voltage (V-oc) of 0.996 V and a remarkably low energy loss of 0.47 eV. The energy loss of 0.47 eV should be the lowest value for the reported PSCs with PCE of over 12%. In addition, by using PBDB-T as a donor to blend with IE4F-S, the PSC device also demonstrates a promising PCE of 13.72%, which is one of the top efficiencies for PBDB-T-based devices. The results demonstrate that appropriate modulation of the main-chain planarity is an effective approach to construct high-performance fused-ring-based acceptors for PSCs.